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Old 01-29-2011, 02:36 PM   #1
David R
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Default Engine Stumble

Hi all, could you some suggestions for trouble shooting.

Have a 97 sw2 automatic with 245000Km on it.

An annoying problem has developed, really hard to diagnose as the event doesn't last long and is dependent on the weather. This has been going since last October, but has become a nearly daily event with Winter in full swing.

The engine has a pronounced misfire or stumble, while warming up. Sometimes while driving, but mostly while idling. Today it hit a new level of misfiring; the stumble lasted long enough to stop the engine. It basically felt like the engine spark stopped long enough that the rpms were to low to recover from. Usually the misfire is a blip or two every couple of seconds or more. If it happens while driving it feels like a momentary loss of power or all the way to the brakes being tapped.

I'll try to paint a really good picture of the conditions needed for this problem. The car must have been sitting for more then 10 hours. The air temperature needs to be near or below freezing (+4C to -10C), with dew or frost having formed on the car. Frost is a bigger problem than dew. Really dry cold air doesn't cause a problem.

The engine will start fine, and idle around 1100-1200 rpm. As soon as the engine is warm enough to bring the idle down to 1000-1100 rpm, the misfires start. My car has a pronounced stepping action for idle when cold, so it would be like the second or third steps down from high idle. The temperature gauge will be reading just under 1/8, when misfiring or stumble will start, very consistent in that respect. The misfiring or stumbling will clear up just under the 1/4 mark on the gauge, again very consistent. Once fully warmed, the gauge is between 3/8 and 9/16, idle is smooth and power seems normal.

Things that have been done, new Air Filter, new Ignition Wires (aftermarket), new Spark Plugs (NGK), Ignition Control Module and Coils removed and cleaned.

Of course while the misfire or stumbling is happening the Engine Light doesn't come on and there are no stored codes either.

Anyone have any ideas?

David

...
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2009 Astra XE 5sp 225K km
2000 Honda Civic SI 5sp 172K km, AKA EX Coupe - Gone
1997 SW2 DOHC Auto 330K km - Parked, waiting for the value of scrape to go up

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Old 01-29-2011, 02:42 PM   #2
oakraiders24
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Default Re: Engine Stumble

A warm engine should be around 750 RPMs at idle. I dont think you are letting it warm up enough. Maybe change the thermostat to 195 degrees version. Are you getting codes?

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Old 01-29-2011, 03:20 PM   #3
David R
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Default Re: Engine Stumble

No Codes, Warmed up; 800 in neutral, 750 in gear.

Thermostat is 195, OBDII software reports 197 to 205 for engine temp when warmed up.

Re: "I dont think you are letting it warm up enough", Um... that is the point, this is what is happening while the car is sitting and idling to warm it up, and occasionally while driving in the first 5 or so minutes.

I maybe wrong, but I was the impression that these cars are basically start and go, just give sufficient time for the oil to flow out to the corners. I do however allow 3-5 minutes on a cold day, typically being 900-1000 before I'm off and running.

David

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Old 01-29-2011, 07:02 PM   #4
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Default Re: Engine Stumble

Quote:
Originally Posted by David R View Post
.... Have a 97 sw2 automatic with 245000Km [147k miles] on it....The engine has a pronounced misfire or stumble, while warming up.....Today it hit a new level of misfiring; the stumble lasted long enough to stop the engine. It basically felt like the engine spark stopped long enough that the rpms were to[o] low to recover from. Usually the misfire is a blip or two every couple of seconds or more. If it happens while driving it feels like a momentary loss of power or all the way to the brakes being tapped....The engine will start fine, and idle around 1100-1200 rpm. As soon as the engine is warm enough to bring the idle down to 1000-1100 rpm, the misfires start....The temperature gauge will be reading just under 1/8, when misfiring or stumble will start, very consistent in that respect. The misfiring or stumbling will clear up just under the 1/4 mark on the gauge, again very consistent. Once fully warmed, the gauge is between 3/8 and 9/16, idle is smooth and power seems normal....
There can a number of things to check with a good engine lasting this long. One may be compression as the cold engine with low compression won't run as well until warmed up. This would require a compression test to verify the condition of this well maintained car. If not compression...............?

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Old 01-30-2011, 12:59 PM   #5
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Default Re: Engine Stumble

Good thought on the compression. I'll do a cold test, then a warm test if I see a significant issue. Have to wait for the parking lot to get a little warmer. I've been thinking I should do one, as I've been putting alot of time and money into the suspension lately. I'm starting to watch for the tipping point.

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Old 01-30-2011, 05:20 PM   #6
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Default Re: Engine Stumble

Well its fair to say that compression isn't the problem. All cylinders read between 220 and 225 cold. Might be a bit of a calibration issue on the gauge, seems wonderfully high.

Also good to know that the time and money I'm putting into the suspension isn't wasted.

...
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2009 Astra XE 5sp 225K km
2000 Honda Civic SI 5sp 172K km, AKA EX Coupe - Gone
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Last edited by David R; 01-30-2011 at 05:31 PM..

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Old 01-30-2011, 06:02 PM   #7
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Default Re: Engine Stumble

Perfect compression, 245k km/147k miles, only slight misfiring during warm-up and disappears in normal running? You mentioned frost allows this condition more than dew. Any chance that the new wires may need some dielectric grease on both ends to help voltage conduction? With a cleaned ignition module and coils, could the high voltage be shorting on cold warm up until this frost has evaporated? Maybe on the coil side? The mounting bolts for the ignition module provides ground so is there any possibility of intermittent connection there? And the blades connecting both coils?

This can be either ignition or fuel related and it seems to be ignition sourced since fuel would have an overall detrimental effect and not target a portion of engine running. At least to my knowledge.

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Old 01-30-2011, 06:20 PM   #8
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Default Re: Engine Stumble

Those compression numbers seem a bit high, actually. That would be perfect for a new engine... unless your engine has been rebuilt, it really shouldn't be that high, anymore (possible, I suppose, but rare). Can you check with a different gauge? In the past year, I've used 3 different compression gauges. Two were very inaccurate (two different loaners from autozone). They both read low, not high, though.

The next thing I would try (if the compression checks out) is coils and ICM. You can get them all together (2 coils and the ICM) from most junkyards for anywhere between $15 and $100. I got mine, a few months ago, for $18. If you search on car-part.com, for a coil/ignitor, that's typically considered both coils and the ICM.

Quote:
Originally Posted by fdryer View Post
Any chance that the new wires may need some dielectric grease on both ends to help voltage conduction?
Dielectric grease doesn't help voltage conduction, it prevents it (that property is mainly to prevent excessive use from creating a short-circuit). It's used to seal connections to prevent corrosion and prevent spark plug wire-boots from fusing to the plugs. While, in theory, it could prevent the spark from "leaking" through the plug boot, this is not its purpose, nor should it ever be necessary. A properly functioning ignition system should work fine 100% of the time with or without it. Assuming the resistance of the wires isn't too high, the path through the wire, plug, engine, second plug, and second wire should be less resistance than jumping all the way to the other coil tower or the transmission.

Check all of the wires for resistance with a multi-meter... perhaps you got a defective one.

Check to be sure all of the wires are on all the way. I went for years without my plug wires on all the way (I guess they were just far enough for the wire's conductor to touch the plug top but not actually be forced onto the top of the plug). They were like that when I got them, and even when I replaced them, I thought that was as far as they went, so I didn't force them further. It ran fine the whole time, but perhaps a bit of ice or something in there could have caused a problem.

...
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Last edited by PlasticCarsRock; 01-30-2011 at 06:34 PM..

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Old 01-30-2011, 07:22 PM   #9
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Default Re: Engine Stumble

Quote:
Originally Posted by PlasticCarsRock View Post
.... Dielectric grease doesn't help voltage conduction, it prevents it (that property is mainly to prevent excessive use from creating a short-circuit). It's used to seal connections to prevent corrosion and prevent spark plug wire-boots from fusing to the plugs. While, in theory, it could prevent the spark from "leaking" through the plug boot, this is not its purpose, nor should it ever be necessary..
Sorry but dielectric grease does have its use.
Dielectric grease is a non-conductive, silicone grease designed to seal out moisture and, therefore, prevent corrosion on electrical connectors. Being non-conductive, it does not enhance the flow of electrical current. This property makes it an ideal lubricant and sealant for the rubber portions of electrical connectors. The widest use of dielectric grease is in high-voltage connections associated with spark plugs. The grease is applied to the rubber boot of the plug wire. This helps the rubber boot slide onto the ceramic insulator of the plug. The grease also acts to seal the rubber boot, while at the same time preventing the rubber from becoming stuck to the ceramic. Generally spark plugs are in located in areas of high temperature, and the grease is formulated to withstand the temperature range expected.

It can be surmised that preventing corrosion from occurring on the coil towers will aid in high voltage conduction as long as the physical contact is made between plug boot and plug. A severely corroded coil tower will not conduct and will cause misfiring as well as voltage conduction through the boot to anywhere close by, especially in any frost/humid/dew conditions. A good example is simply placing a hand on the plug wires in early morning frost/humid/dew conditions; if you're shocked, guess why? High voltage will always take the shortest path of least electrical resistance to ground. Wet plug boots/hand/nearby engine block. If you've see some members pics showing severely corroded coil towers you'd understand the reasoning for using dielectric grease; as a corrosion preventative that aids in long term corrosion prevention otherwise it wouldn't have been invented. Misifiring is a direct result of severely corroded coil towers as well as dry rot on plug wires. Add any moisture to this recipe and misfire results.

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Old 01-30-2011, 07:54 PM   #10
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Default Re: Engine Stumble

Quote:
Originally Posted by fdryer View Post
Sorry but dielectric grease does have its use.
Correct; I was a bit unclear. I meant it should never be necessary to keep a car running. It is very helpful as "preventative maintenance" to keep things from corroding, etc. It's also helpful to keep spark plug wires from sticking to the plugs as I've heard can happen.

My point was that if it won't run without dielectric grease, adding the grease is not a fix. If it helps anything, it's likely just a band-aid, masking the problem.

I try to use it whenever possible, but few people really do.

...
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Old 01-30-2011, 08:06 PM   #11
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Default Re: Engine Stumble

Me too, but then again I don't have plug wires. I have to suffer dismantling parts of the intake system to even see my spark plugs.

The OP's very specific misfiring only occurs at the beginning of cold warm ups and disappears altogether after warm up. Its the only reason I brought up dielectric grease as (you called it) a band aid. I would think if it corrected the misfiring then either leave it at that or..................replace the ignition parts? If this were mine I'd leave it as a cure and just stay aware of it if it occurs later. Perhaps better cleaning of the ignition parts will help to eliminate it altogether and dielectric grease will help for corrosion prevention as originally designed.

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Old 01-30-2011, 10:52 PM   #12
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Default Re: Engine Stumble

Not sure if this is your problem, but I just had a problem like this on my 2002 saturn SL1, when pulling out of my driveway on the cold mornings the engine as i gave it gas it would make a very noticable stumble then regain itself, the problem I had was a dirty EGR valve, the pintle valve was carboned up and sticking slighty open and allowing egr gases to mix with the intake gases when it wasnt suppose to, you could have a dirty EGR valve and is slighty stuck open, try that if all else fails.

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Old 01-30-2011, 11:05 PM   #13
David R
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Default Re: Engine Stumble

Yes its very likely that the calibration is off on the compression gauge. Balance and high being of more importance in this case, rather than absolute reading. The gauge has been used else where, giving reasonable results, so I have no reason to believe its grossly off, perhaps 5-10 lbs in error. Perhaps with it being about -8C after a night of -12C, oil will be getting thick, this would have also contributed to elevated readings as well.

On the previous set of wires I had been using dielectric grease, was a bit of a pain because the air seal formed on the towers would cause the boots to slide up the towers if I wasn't careful. The last set of wires, I think number #4 wire, was jumping to the EGR body. I've found the aftermarket wire sets are to long, so creative routing is required. The towers were cleaned and the tips are good, but the laminations are getting rusty. I may seek out replacements at a J/Y.

The stumble or misfire doesn't occur when the engine is dead cold, but after things are just warming up, when the idle is being lowered by the PCM.

Its going to be -18C overnight, so it will probably be frost free. I might try a mister and see if I can provoke some trouble.

...
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Old 01-30-2011, 11:11 PM   #14
David R
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Default Re: Engine Stumble

Interesting point SL19302.

This car does see a lot more city driving than it used to, might be a carbon build up.

I'll check that tomorrow, if the weather permits

...
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Old 01-30-2011, 11:33 PM   #15
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Default Re: Engine Stumble

Quote:
Originally Posted by SL19302 View Post
the problem I had was a dirty EGR valve
+1

Don't know why we didn't think of it earlier. EGR valve can cause that exact problem. You can take if off and clean it with some carb-cleaner (or similar). However, if the problem is still present, it could still be the egr valve. Best way to narrow it down in one step is to temporarily block off the egr valve completely. There's a richpin video that shows how to make a block off gasket from an old soda can. See: http://www.youtube.com/watch?v=8YRq2Xl58Oo

For cleaning, see: http://www.youtube.com/watch?v=bt5lRTt6BsU

If the problem is gone with the block-off, you should try cleaning the valve. If it stays away, you've fixed it. If not, your best bet might be a junkyard EGR. From the parts-store, they're around $100.

...
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Old 02-02-2011, 04:58 PM   #16
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Default Re: Engine Stumble

I've had this happen with other vehicles, and it turned out to be the EGR valve. If it opens at idle (it's not supposed to) the engine will stumble severely or stall.

EASY: Try pulling off the electrical connection on the EGR and running the engine (You'll probably get a check engine light). See if the trouble goes away. If it does, the EGR is bad.

A LITTLE HARDER: Cut a piece of metal and bolt it between the EGR and the engine. If the trouble goes away, your EGR is bad.

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Old 02-05-2011, 12:48 PM   #17
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Default Re: Engine Stumble

Ok, so I've had an opportunity to run with the EGR blocked. Used the zip-lid from a cat food can, lot less fuss. Anyway it certainly has an effect, but its not the only problem. The car runs much better during cold idle, has more power, and may well be getting fuel economy as well. This car has always had less than stellar fuel economy, but particularly lame fuel economy in the city.

The big however is, the engine does still stumble in that narrow band of conditions while warming up. The stumble isn't as deep as before, feels more like a misfire now. Engine's rpms pop-up after a misfire, which it didn't do before, kind of curious. While driving, not fully warmed, there is still the occasional blip, almost not perceptible, compared to tapping the brakes as before.

My conclusion is that the EGR valve isn't fully closing, and may have been this way for a very long time. Mechanically it seems fine, spring action is good. Very little carbon, certainly no clumping or obstructions. The pintle just appears to stop early. I'll have to give it the works for cleaning and see if that helps.

I have recently had one incident with the engine stalling when fully warmed up. Sitting at a stop light, the engine just stopped as if I'd turned it off in gear. It started right up again no problem. Temperature gauge was at 3/8ths.

David R

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Old 02-05-2011, 02:54 PM   #18
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Default Re: Engine Stumble

With the egr valve blocked off and you noticing improved performance but still having hesitation/stumbling, it seems to be more than one problem so eliminating the egr valve for now helps tremendously. If I stated it before, I'm under the impression that worn out parts are going to be difficult to isolate. In addition to egr valve cleaning or replacement, other sensors may be in similar conditions that can either use cleaning or replacement. Finding the elusive sensor may be difficult. Off the top of my head would be the map and crank position sensor. Cleaning the map sensor is about all you can do where the little port hole may be covered and restricting readings of manifold pressure in freezing conditions. The cps is a stretch (for failure) since you can restart immediately but not ruling out out completely.

Egr valve cleaning may require careful cleaning, perhaps something like toothpaste/lapping compound on the pintle shaft to scrub off hard deposits that may make it difficult to slide open/closed and contributing to closing completely to prevent exhaust gases into the intake manifold at idle rpm.

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Old 02-05-2011, 09:50 PM   #19
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Default Re: Engine Stumble

You're right this is going to be about compound issues.

The EGR must have been a problem for quite awhile, not revealed until another issue came up which resulted in a whole greater than its parts.

I'd leave the EGR blocked for the time being, but the check engine light came on this afternoon, so I guess not. I haven't checked yet, I assume the code is EGR realeted, possibly a failed diagnostic emmissions cycle.

The CPS has crossed my mind, for that all cyclinders missing effect.

The MAP was changed a year and a half ago because the original was reading pretty far off for ambient pressure.

I need to find a J/Y that I can fill a basket with sensors.

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Old 02-06-2011, 12:30 AM   #20
1996SL11.9L
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2002 SL1
Default Re: Engine Stumble

clean your Throttle body and idle air passage, (as well as the pintle for the IAC) block off the egr again (or continue too) pull the PCM"B" fuse for a while to kill the memory restart and see what happens. It will have to remap some things so give it a couple of drive cycles.

If the coil plates are starting to delaminate from rust they ought to be replaced......... have an ICM and or two and some coil packs thrown in the box of sensors also.

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